The big concern with filesystems becoming corrupt is that all of the data can be lost on a filesystem. Most of the time, this doesn’t show up, but if you lose power at just the wrong time, it can happen. With FAT, HFS, ext2, and similar filesystems that were vulnerable to corruption on power loss, that was a real risk.

So having some kind of power source to make an unclean shutdown unlikely avoids the risk of a really, really bad scenario.

The general shift away from reliance on those filesystems has mitigated the really-bad-case that drove a lot of UPS use.

Databases are probably the most-critical case where applications update a file on disk constantly, and where corruption would be bad. As long as they live on a filesystem that itself can’t become corrupt on power loss, they’re normally structured with a carefully-ordered series of writes and use of write barriers so that they cannot become corrupt.

An individual file can be partially written out. Like, say I’m saving a file in Photoshop, and I have only written half of that file. What winds up on the disk is the first half of of a Photoshop file. That’s an invalid Photoshop file. For some applications, that can matter. Like, say (a) I chose to overwrite an old file and (b) the application doesn’t atomically store the new file (like, write it out, fsync(), and then rename the new file over the old) and © there’s no backup or other system in place.

Or, even aside from partially writing out a file, I can entirely lose work that isn’t saved at all, if I’m not using a software package that makes use of some sort of autosave system. If I haven’t saved all day, then, well, all of that unsaved work is going to go away if there’s a power loss.

That’s a much smaller potential data loss, but, sure…power loss can cause data loss, even if it doesn’t produce that “everything is lost” filesystem corruption.

I’m not asserting that there’s no utility to a UPS; quite the contrary, as my comment was explaining to OP why there is use some people have for having NUT even if he personally doesn’t care much about it for his use case. I’m just pointing out that some of the major reasons for having a UPS+host-side-software combination that existed in, say, the 1990s aren’t really much of a thing in 2026. That was that you really did not want machines using filesystems normally used then to perform an unclean shutdown. Even with a UPS and host-side software like NUT, you can have data loss, as NUT cannot force all software to save unsaved data; there’s no standardized mechanism for forcing applications to save. If the PC is attended, you might get a warning and have a chance to manually save, but that’ll be the best that’ll happen, and if the PC is unattended, well, that save isn’t going to happen. But what NUT and similar software can do is to, when the UPS battery level gets low, trigger a clean shutdown. That ensures that the OS has time to perform a clean shutdown, and on filesystems that have a risk of filesystem corruption if the power is cut—FAT, HFS, ext2, and similar—a UPS with host-side software would avoid that case from arising.

If someone wants to have a UPS in 2026 on filesystems that don’t have those limitations, that’s fine. They may want to have, say, a five minute window to save their work if they are at the PC when power loss occurs. It may help avoid problems that arise from software that cannot cleanly handle power loss—I that Steam can, if power loss occurs while it is updating itself, wind up in a broken state from which it cannot automatically recover when restarted, as I’ve done that myself.

But generally, if you lose power on a system in 2026, you aren’t facing a “I might lose the contents of my hard drive” scenario.